Hitherto, fine patterning by lithography using photoresist compositions has been performed in processes of manufacturing semiconductor devices, such as ICs and LSI. In recent years, increasing need for larger packing densities of integrated circuits has come to entail superfine patterning in the submicron or quatermicron region. In response to such a requirement, the light sources used in photolithography are showing a tendency to have shorter wavelengths. Actually, the exposure light used has been changed from g-ray to i-ray, and further to KrF excimer laser beam. And nowadays the development of lithographic processes using not only excimer laser beams but also electron beams and X-rays is proceeding.
Electron-beam lithography in particular is placed as a next-generation patterning technology or a generation-after-next patterning technology, and it is desired to develop negative resist highly sensitive to electron beams and capable of forming highly resolved patterns. Enhancement of resist sensitivity is a very important problem in pursuing reduction of wafer processing time. As to the electron-beam negative resist, however, pursuit of increased sensitivity causes a worsening of line edge roughness in addition to reduction of resolution and deterioration in pattern profile, thereby resulting in a problem of greatly reducing yield rates of devices. Therefore, it is strongly desired to develop resist compositions satisfying those quality requirements at the same time. The term “line edge roughness” as used here in means rough appearance the pattern-substrate interface edge has when resist patterns are viewed from right above, wherein the roughness of the pattern-substrate interface edge arises from irregular fluctuation in a direction perpendicular to the line direction that is attributed to resist properties. Transfer of this roughness occurs in the etching process using the resist as a mask and gives rise to deterioration in electric properties and decrease in yield rate. High sensitivity bears a trade-off relation to high resolution, pattern profiles of good quality and satisfactory line edge roughness, and so how to satisfy these properties at the same time is a very important problem.
As resist suitable for such electron-beam and X-ray lithographic processes, chemical amplification resist utilizing mainly an acid catalyst has been mainly used from a sensitivity-oriented point of view. With respect to negative resist of this type, chemical amplification resist compositions containing mainly an alkali-soluble resin, a cross-linking agent, an acid generator and additives have been used effectively.
Various studies to improve performances of chemical amplification negative resist have been made from the viewpoint of focusing attention on cross-linking agents. For instance, the cross-linking agents of glycoluril type, the cross-linking agents of hexamethoxymelamine type, the cross-linking agents having urea skeletons and the phenolic cross-linking agents containing polynuclear phenol skeletons are disclosed in JP-A-2-15270, Japanese Patent No. 2985968, Japanese Patent No. 2861309 and JP-A-2001-51417, respectively.
In the superfine regions, however, any of hitherto known cross-linking agents including the above-cited ones were unsuccessful in satisfying all the performance requirements, namely high sensitivity, high resolution, good-quality pattern profile and satisfactory line edge roughness.